aldol condensation reactions

...to give β-hydroxy aldehydes. The prototype of this reaction is the conversion of acetaldehyde to β-hydroxybutyraldehyde, or aldol. The first step of this reaction is the production of an
enolate ion (as in formation of the keto–enol tautomeric mixture), but this anion then reacts with a second molecule of acetaldehyde to give the product as shown below:

carbanion

Closely related to the allyl carbanion are the enolate anions, in which one of the carbon atoms is replaced by an oxygen atom. Enolate ions are derivatives of ketones and aldehydes (compounds containing a double bond between carbon and oxygen atoms), from which they can be generated by abstraction of a proton from the carbon atom that is located next to the carbon of the carbonyl group. The...